Many devices require a knob with an illuminated indicator to communicate information relating to the function or operation of the knob or device with which it is associated. For example, illumination can be used to communicate the position of the knob or the state of the device. Knob illumination has traditionally been accomplished by the use of a stationary light source and light directing light pipes. A light pipe typically consists of a light transmitting plastic. The light pipe directs illumination from a light source to an illuminated destination by reflecting the light along the interior of the light pipe. The light source is placed in a stationary location, and the illumination from the light source is directed by internal reflection through the light pipe to the interior of the knob or, specifically, to an indicator window of the knob.
As the knob rotates, slides, or is otherwise operated, the position of the light pipe within the knob changes relative to the stationary light source thereby varying the reflection angles traversed within the light pipe. Consequently, the quality or intensity of the illumination provided by the light pipe may vary as the knob is operated.
Light source leads are typically not sturdy. Thus, an electrical connection to light source leads must be sufficiently stable such that the electrical connection is not disrupted by vibration or friction caused by the operation of the knob.
The design of devices utilizing illuminated knobs is often hampered by the unpredictable nature of the stationary light source and light pipe configuration. Device design may require revisions as the knob and light pipes are adjusted through trial and error, resulting in additional design time and cost.